The Pathology Core is responsible 1) for accrual of residual material not required for diagnosis from human melanoma and nevi to be supplied to the Cell Line and Antibody Core for use in the Projects; 2) for the development of immunohistochemical and in situ hybridization methods to enable the identification of antigens or mRNAs in archival and freshly- isolated tissues. Many antibodies and/or probes of relevance to the projects mentioned above are available in fixed or frozen tissues. The Core has access to a very large collection of human (23,000 accessions/year) and of dermatology (50,000). The database of the Pigmented Lesion Group including glass slides of virtually all of the greater than 4000 cases of primary accrued by the Group since 1972 is available to the Core for analysis of attributed to be used in model building, and for selection of blocks to be retrieved from the permanent archives of our own laboratories and of contributing laboratories Expertise in all aspects of the pathological diagnosis and classification of melanocytic neoplasms is provided to the projects on a continuing basis.